What Car? investigates: tyre safety - Introduction

Everyone knows that worn tyres are lethal, but did you know that under-inflated tyres can be equally deadly? They'll do some serious damage to your wallet as well.

While tyre pressures are crucial to safety and economy, they're often overlooked by motorists. A recent whatcar.com poll found that only one driver in 10 checks their tyre pressures the recommended once a week.

Even more worryingly, half said they check pressures only every six months - or less.

In addition, a nationwide inspection survey by Michelin revealed that a shocking 80% of cars on British roads are running with incorrect tyre pressures.

It's not just a PSI here or there, either - 36% had at least one tyre between seven and 12PSI below the correct pressure. A further 15% were found to be at least 14PSI under - around half the correct pressure for most tyres.

The problem is that even something like a plunge in ambient temperature can drop the PSI significantly, and a quick glance or a kick isn't enough to tell apart a dangerously under-inflated tyre from a safe one.

In our tests, the pressure in some tyres could be dropped to as low as 10 pounds per square inch (PSI) - a third of the recommended level - before it was obvious that they were under-inflated.

With people paying so little interest in the simple maintenance required for their car's tyres, we had to find out how much of an effect low pressures have on safety and economy.